Tolokonnikova's husband has said he was told by prison officials that the musician could be moved to a prison colony in Siberia, according to Amnesty International.

The musician is currently serving a two-year jail sentence for hooliganism motivated by religious hatred, due to holding a concert at a Moscow church.

Amnesty Interntional's Europe and Central Asia deputy director Denis Krivosheev said of her current condition: "Nadezhda Tolokonnikova has publicly complained of threats she received from prison officials. We are concerned that she now may be being punished for this and for speaking out about deplorable prison conditions.

"The Russian authorities must immediately tell her family where she is and allow her access to a lawyer. She is a prisoner of conscience who should have never been taken to jail in the first place. Refusing to say where she is simply fuels rumours of the worst case scenario."

Krivosheev concluded: "If reports are true, transferring her to a prison colony thousands of kilometres from Moscow would make it almost impossible for her relatives and lawyers to see her. This would be a violation of her human rights and of Russia's own laws."